Citrobacter freundii (C. freundii) is an organism which occurs in water, food, feces, and urine. The organism is throught to be found constantly in healthy persons. Certain serotypes apparently cause sporadic infections of alimentary and urinary tracts, and infections of gall bladder, middle ear, and meninges have been reported. The presence of this organism in urine is a reliable indicator of a urinary tract infection. If C. freundii is present in a given sample of urine, it is possible that Aeromonas and Klebsiella also are present.
The medium of this invention is an improved medium designed for use with the optical detection system disclosed in U.S. applications Ser. Nos. 255,533 filed May 22, 1972 now abandoned and 461,249 filed Apr. 16, 1974 now U.S. Pat. No. 3,963,355 and in the improved device disclosed and claimed in applications filed on even date herewith by Charles, Jones, Staples and Wiegner entitled AUTOMATED MICROBIAL ANALYZER and MACHINE AND PROCESS FOR READING CARDS CONTAINING MEDICAL SPECIMENS. These applications describe mechanism and apparatus suitable for analyzing specimens for specific microorganisms using a plastic tray or card which contains a series of dried culture media contained in separate but connected cells, each of the media being specific to a single organism. When the sample is inserted into the card, mixed with the media in the cells, and incubated in the machine, the organism (or organisms) present in the specimen interacts with the culture medium specific to that organism and produces a change in the medium which is read by the machine to indicate the presence of that organism. The change in the medium involves a change in the light transmitting properties of the medium, i.e., a color change or change in turbidity. The change may be caused by metabolic activity of the organisms, which, for example, may cause production of acid and a change in pH which causes a color change in a pH sensitive indicator in the medium. The change in the light transmitting properties of the medium also may be caused by a precipitate forming in the medium due to metabolic activity of the organism or it may be caused by growth of the organism.
The specific media designed for use in the aforesaid cards are all designed to favor growth of one microorganisms, are capable of being freeze dried, and can function in the low 0.sub.2 environment of the wells of the card described in detail in said copending applications AUTOMATED MICROBIAL ANALYZER and MACHINE AND PROCESS FOR READING CARDS CONTAINING MEDICAL SPECIMENS.
I have discovered a medium which can selectively identify C. freundii organism in urine when the medium is placed in the wells of the cards described in application AUTOMATED MICROBIAL ANALYZER.
Positive results are indicated by means of a precipitate formed in the clear medium which causes a change in the light transmitting character of the medium, which change is read by the mechanism described in application AUTOMATED MICROBIAL ANALYZER. The entire test can be completed within 8-12 hours, whereas current methods of detection require from about 36 to about 48 hours.